Incubation Period, Spore Shedding Duration, and Symptoms of Enterocytozoon bieneusi Genotype C Infection in a Foodborne Outbreak in Denmark, 2020

Enterocytozoon bieneusiwas identified as the cause of a foodborne outbreak of diarrhea affecting >70 individuals. The incubation period was 5-12 days. Spores were shed in stool for up to 43 days after symptom onset. Background Microsporidia are rarely reported to cause outbreaks of diarrhea. We describe a foodborne outbreak of microsporidiosis from a workplace canteen in November 2020 in Denmark. Methods A probable case was defined as any person using the canteen between 4 November and 13 December 2020, reporting at least one gastrointestinal symptom, whereas a confirmed case also had an Enterocytozoon bieneusi positive stool sample. A web-based questionnaire was used to collect clinical, epidemiological, and food exposure data. We performed a retrospective cohort study and tested stool samples from affected individuals for bacterial, viral, and parasitic pathogens, including E. bieneusi. Results Altogether, 195 individuals completed the questionnaire. We identified 52 cases (65% male; median age 45 years [range 25-65]). Diarrhea (90%), fatigue (83%), and abdominal pain (79%) were the most commonly reported symptoms. Eight cases were laboratory-confirmed and had E. bieneusi genotype C. The incubation period was between 5 and 12 days, and polymerase chain reaction (PCR)-detectable spore shedding occurred up to 43 days after symptom onset. Disease was associated with consuming food from the workplace canteen on 4 November 2020 (relative risk [RR[, 2.8 [95% confidence interval [CI]: 1.4 - 5.4]) and lunchboxes containing open sandwiches (RR, 3.2 [95% CI: 1.4 - 7.2]) served that day. Conclusions This is the second documented foodborne outbreak of E. bieneusi genotype C-associated diarrhea worldwide. Epidemiological findings advocated an open sandwiches lunchbox from 4 November 2020, as a likely source. E. bieneusi may be an under-reported cause of outbreaks of diarrhea, and testing for it might be useful in foodborne outbreak investigations.